Evolution of Life Cycles of Nematodes Parasitizing Woody Plants As a Result of Ecological and Phylogenetic Co-Adaptations with Hosts and Vectors

Abstract

Fundamental aspects in the evolution of nematodes parasitizing woody plants are reviewed. (1) Nematode faunal lists of natural refugia are useful to predict the risks of opportunistic pathogens becoming true pathogens in the forest and park communities. (2) Nematode composition in natural refugia gives a chance to identify nematode antagonists of insect vectors of dangerous fungal and nematode infections, which can be potentially used as the biological agents for woody plants’ protection. (3) Dauers in the ancestors of wood-inhabiting nematodes played a role as a survival stage in the detritus decomposition succession, and they later acquired the functions of dispersal and adaptations for transmission using insect vectors. (4) When inspecting wilted trees, it is necessary to use dauers for diagnostics, as sexually mature nematodes may be absent in tree tissues. (5) Plant parasitic nematodes originated from members of the detritus food web and retained a detritivorous phase in the life cycle as a part of the propagative generation. (6) Vectors in the life cycles of plant parasitic nematodes are inherited from the ancestral detritivorous nematode associations, rather than inserted in the dixenic life cycle of the ‘nematode–fungus–plant’ association. (7) Despite the significant difference in the duration of the nematode–tree and nematode–vector phases of the life cycle, the actual parasitic nematode specificity is dual: firstly to the vector and secondly to the natural host plant (as demonstrated in phytotests excluding a vector).